I found this enlightening article on the internet:
Feeling down in the dumps and having the blues is not reserved just for big holidays like Christmas, Easter and the Fourth of July. There are many anniversary dates that remind us of something or sometime in our life that made us feel depressed.
The death of someone close to us, our divorce date, our marriage date, a birthday, etc. We may not be able to wipe out the memory of these events but we can take charge of how we feel about them.